This invention relates to spiral gearing of the ball circulation type used, for example, in steering systems for motor vehicles and for vehicle brake actuators.
Ball circulation types of spiral gearing always include a spiral or screw gear and a nut between which a plurality of spherical elements or balls are disposed in a spiral shaped groove.. Rotation of the spiral gear by a manual steering wheel through a steering spindle, e.g., thus results in an axial shift of the nut. The balls traveling through the spiral shaped groove or ball guiding channels of the gear are returned from one end of the guiding channels to the other by a ball return tube disposed within a peripheral slot in the nut. In order to maintain the proper position of the ball return tube for guiding safe return of the balls, a spacer is generally disposed between the ball return tube and a cover enclosing the peripheral slot in the nut. The cover wall surrounding the nut, such as the cylinder or steering housing of a motor vehicle steering system, holds the spacer and the ball return tube within the nut between the two ends of the ball guiding channels.
In assembling the ball circulation type spiral gearing, the ball return tube was heretofore intoduced into the peripheral slot of the nut and thereby plugged into the ball guiding channels at the two ends thereof. The spacer was then separately inserted above the ball return tube and the screw gear installed. This method of assembly has certain drawbacks. During assembly, one sometimes forgets to insert the spacer. Although the spiral gearing will initially function despite the absence of the spacer, during subsequent operartion the ends of the ball return tube slip out of the ball guiding channels without being detected. In such event, the balls escape from the ball guiding channels and the gearing eventually becomes inoperative. In a steering system, this leads to failure wihtout any prior indication.
It is therefore an important object of the present invention to provide spiral gearing of the ball circulation type which will prevent the aforementioned drawback or problem in the assembly of such gearing.